When 10 AWG THHN/THWN copper conductors are connected to a 15-amp circuit breaker, what is the rating of the branch circuit?

In this scenario, the rating of the branch circuit is primarily determined by the rating of the circuit breaker, which is set at 15 amps. The circuit breaker is a safety device designed to protect the conductors in a circuit from overcurrent, and its rating dictates the maximum current that the conductors can safely carry without tripping or causing potential damage.

While it is important to note that 10 AWG THHN/THWN copper conductors can handle higher currents—generally rated for up to 30 amps under normal conditions—the circuit breaker serves as the defining limit for the branch circuit's rating in this case. Therefore, the circuit is effectively limited to 15 amps.

This configuration ensures safety; if an overload occurs, the breaker will trip and open the circuit to prevent overheating and potential fire hazards, even though the conductors could handle more current. Thus, the rating of the branch circuit matches the circuit breaker rating of 15 amps.